The cytochalasins are a group of cytotoxic fungal metabolites which exhibit a complex array of biological activities. These molecules have been used extensively as probes of cell biological processes. The specific objectives of our investigation are: (1)\the design and synthesis of simplified cytochalasin analogs into which 13C-labels, fluorophores, affinity labeling functionality, and/or modified functional groups have been incorporated; (2)\the determination of specific structure-activity correlations of simplified cytochalasins; (3)\determination of the specific molecular aspects of actin polymerization; and (4)\identification and characterization of cellular cytochalasin receptors. Efficient synthetic strategies have been developed to prepare functionally versatile perhydroisoindolones from which a variety of simplified cytochalasins are being prepared. Among these simplified cytochalasins are 13C-labeled, fluorescent or affinity labeling reagents. Assay methods to assess biological activities of these molecules include a cell-free gelatin assay and a fluorescence photobleaching recovery (FPR) assay. NMR and FPR methods are being employed to elucidate the mechanisms of actin polymerization and the specific molecular interactions of cytochalasins with actin. It is anticipated that these structurally simplified analogs will exhibit a more well-defined spectrum of biological activities, enabling delineation of specific molecular events involved with membrane and cytoskeletal processes. (L)